1. Field of the Invention
The invention relates to a method for manufacturing a long-range radio frequency identification metallic product and a structure thereof, providing long-range reading and transmitting effects and preventing the RFID from being duplicated.
2. Description of Related Art
Radio Frequency Identification (RFID) skills have been widely applied to various fields such as industrial automation, commercial automation, traffic and transportation control management. With the increasing researches related to ultra-high-frequency (UHF) RFID systems, long-range reading and transmitting effect, high efficiency and low cost of RFID skills can be realized. Therefore, with the advantages such as non-contact, low cost, advanced anti-counterfeit and mass-production, the RFID skills has gradually replaced conventional two-dimensional bar code skills in the present markets.
In general, due to microstrip antennas themselves defectively characterized with narrow band limitation, the majority of microstrip antennas can be limitedly designed as single-frequency and narrow band responses. Taking ultra-high frequency electronic tags, which generally incorporated with printed antennas and mostly being microstrip antennas and printed dipoles, for example, due to signals transmitted from the electronic tags being easily reflected by metallic surfaces to cause signal-receiving abnormalities or even non-motions and signal reading problems, it can be appreciated that the ultra-high frequency electronic tags are actually not suitable for being used in an environment surrounded with metallic objects, such as metallic labels, automobiles, motorcycles, vehicle license plates and electric power facilities. Alternatively, the ultra-high frequency electronic tags, are majorly applied to non-metallic medium surfaces of general merchandise, commodities and books. Basically, the majority of improved electronic tag antennas used for metallic surfaces are based on the conventional electronic tag antennas and skills, such as increasing the size of the electronic tag antenna or increasing the metallic surface distance to reduce the undesired effects to the electronic tag antenna caused by the metallic reflective surfaces, or adopting the standardized slotting method to combine with the electronic tags. In the method of increasing the size of the electronic tag antenna or increasing the metallic surface distance to reduce the undesired effects to the electronic tag antenna caused by the metallic reflective surfaces, the height or distance between the electronic tag and the metallic surface shall be kept over than 2.5 mm. In this way, the reading distance of the electronic tag can be increased, but the total cost of the electronic tag is increased and the bandwidth of the antenna is reduced, and also the undesired effects to the electronic tag antenna caused by the metallic reflective surfaces still cannot be eliminated. In view of this, the conventional electronic tag antennas are almost applied for the places with non-metallic surfaces. For example, Electronic Toll Collection (ETC) in Taiwan and the designs of general identification tags. On the other hand, in the combination technique of the standardized slotting method and the electronic tags, the reliability and smoothness of the product are relatively unstable and uncontrollable, and particularly the joint points between the chip and the metallic contacts of the metallic antenna are separated from each other due to the property of thermal expansion and cold shrinkage and long-term operation. In this design, impedance matching shall be performed between each of the metallic antennas and the chip, or the frequency bias or field pattern variations are possibly occurred. In general, joint points between the chip and the metallic contacts of the metallic antenna are treated by conductive glue adhering, copper pouring, copper electroplating and vacuum copper sputtering, etc. Taking the conductive glue for example, the lift span of the conductive glue in the room temperature is about two to five years. If the conductive glue is hardened or oxidized, a certain resistance is formed in the bonding layer disposed between the hardened conductive materials and the neighboring materials in the conductive glue, and the resistance of the accumulated conductive materials in the conductive glue results in the rising of the VF value and a bulky change of the frequency bias and field pattern variation. Thus, it is difficult to control the credibility of the conductive glue with respect to lift span and temperature. The problems caused by the copper pouring method are slightly similar to that of the conductive glue adhering method. In the copper electroplating method, due to the different expansion coefficients of aluminum material and the copper material, the chip and the metallic antenna are possibly separated from each other caused by the peeling of the electroplated copper layer. In the vacuum copper sputtering method, the vacuum copper sputtering method has a stability superior to the copper electroplating method, but the operation cost is extremely high when dealing with the large-sized product with a small sputtering area. Besides, when the electronic tag is combined to the antenna by the standardized slotting method, it is usually that the connection of the electronic tag and the antenna cannot be prevented from crashing, scratching, moistening and stealing.
Ceramic dielectric microstrip antenna is applicable to metallic surfaces, capable of providing high dielectric constant to obtain a minimized antenna size and utilizing the metallic surface as an extended reflective surface to stabilize the performance and to increase directivity, but not suitable for being the economic electronic tag due to its high manufacturing cost. Alternatively, an artificial magnetic conductor (AMC) structure, characterized with high impedance to generate a magnetic-flow direction between the AMC structure and the economic electronic tag identical to that between the metallic surface and the AMC structure, can be laminated between an antenna radiation surface and the metallic surface to increase the reading range and gains of the economic electronic tag, but the AMC skills are still in experimental stage due to its difficulty and high cost.